[LOG4J2-3805] NamedInstantPatternTest#compatibilityOfLegacyPattern fails in timezones with minute offsets (e.g., GMT+05:30) (#3888)

* [LOG4J2-3805] Skip compatibilityOfLegacyPattern test for fractional timezone offsets

The compatibilityOfLegacyPattern test fails in environments where the system
default timezone has a non-zero minute offset (e.g., Asia/Kolkata, Asia/Kathmandu).

Root cause:
- SimpleDateFormat's X pattern truncates fractional offsets (e.g., +05:30 → +05).
- DateTimeFormatter's X pattern preserves the minutes (+05:30).

Since Log4j intentionally follows DateTimeFormatter’s behavior, the test should
not assert equivalence in such environments.

This change adds an assumption to skip the test when the system timezone offset
is not a whole hour. This ensures deterministic builds for contributors in all
regions, while still verifying correctness in whole-hour zones.

Closes #3805

* LOG4J2-3885: Add test for ISO8601_OFFSET_DATE_TIME_HH with system default zone

Ensure legacy and modern formatting produce consistent results
when the system default zone offset is a whole hour.
Skip the test otherwise using assumptions.

Author: ramanathan1504

log4j-core-test/src/test/java/org/apache/logging/log4j/core/pattern/NamedInstantPatternTest.java

@@ -17,8 +17,11 @@
 package org.apache.logging.log4j.core.pattern;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assumptions.assumeThat;
 
 import java.time.Instant;
+import java.time.ZoneId;
+import java.time.ZoneOffset;
 import org.apache.logging.log4j.core.time.MutableInstant;
 import org.apache.logging.log4j.core.util.internal.instant.InstantPatternFormatter;
 import org.junit.jupiter.params.ParameterizedTest;
@@ -29,6 +32,15 @@ class NamedInstantPatternTest {
     @ParameterizedTest
     @EnumSource(NamedInstantPattern.class)
     void compatibilityOfLegacyPattern(NamedInstantPattern namedPattern) {
+        if (namedPattern == NamedInstantPattern.ISO8601_OFFSET_DATE_TIME_HH) {
+            ZoneOffset offset = ZoneId.systemDefault().getRules().getOffset(Instant.now());
+            assumeThat(offset.getTotalSeconds() % 3600 == 0)
+                    .withFailMessage(
+                            "Skipping test: ISO8601_OFFSET_DATE_TIME_HH requires a whole-hour offset, but system offset is %s",
+                            offset)
+                    .isTrue();
+        }
+
         InstantPatternFormatter legacyFormatter = InstantPatternFormatter.newBuilder()
                 .setPattern(namedPattern.getLegacyPattern())
                 .setLegacyFormattersEnabled(true)
@@ -40,6 +52,8 @@ void compatibilityOfLegacyPattern(NamedInstantPattern namedPattern) {
         Instant javaTimeInstant = Instant.now();
         MutableInstant instant = new MutableInstant();
         instant.initFromEpochSecond(javaTimeInstant.getEpochSecond(), javaTimeInstant.getNano());
-        assertThat(legacyFormatter.format(instant)).isEqualTo(formatter.format(instant));
+        String legacy = legacyFormatter.format(instant);
+        String modern = formatter.format(instant);
+        assertThat(legacy).isEqualTo(modern);
     }
 }